This invention relates to electromechanical printers of the type having a rotary print wheel mounted on a translatable carriage, commonly known as "daisy wheel printers".
Printing devices are known which employ a rotary print wheel mounted on a carriage for translation across the width of the print throat area for character printing. The carriage is typically mounted for sliding movement along a pair of spaced guide rods arranged in parallel fashion to the axis of a rotatable platen, and the print wheel is typically removably carried by the output shaft of a motor mounted to the carriage for translation therewith. A print hammer assembly is typically mounted above the print wheel motor, along with a support plate and driving mechanism for a removable ribbon cartridge. The removable ribbon cartridge typically contains either an endless ribbon or a ribbon mounted on a pair of reels. These mechanical mechanisms are typically contained within a printer housing, along with a carriage drive motor, motion translation mechanisms such as belts or cables and pulleys mechanically coupled between the carriage drive motor and the carriage, a platen stepper motor, a motion translating mechanism coupled between the platen stepper motor and the platen for providing paper feed around the platen, a paper deflector and pressure rollers, a mechanism for operating the platen pressure rollers, various switches and the electronic circuitry required to operate the mechanical components of the printer.
In the past, a typical printer construction consisted of a base plate and several individual support plate members for providing the necessary stationary and rotary support for the various mechanical elements of the printer. Due to the close mechanical tolerances required in such a construction to provide high quality printing, a major cost component of known printers has been the individual mechanical support elements employed. This has added unnecessary cost to the manufacturing process. In addition, the assembly time required for a myriad of support pieces has further increased the cost of manufacturing such printers. Moreover, due to the fact that such printers are designed for maximum use at relatively high speed, mechanical vibrations attendant upon such operation, when combined with a relatively large number of individual mounting support and interconnect parts connected together by means of threaded fasteners, exhibit a tendency to cause the mechanical elements to lose their firm, close tolerance mechanical interconnections, with a resulting deterioration in performance and the requirement for frequent service intervals.
Another problem associated with "daisy wheel printers" lies in the requirement for electromagnetic radiation shielding, shielding from static discharges and provision for a thermal mass capable of conducting away from the interior of the printer housing substantial quantities of heat generated by the electrical power components required to operate the system. The requirement for electromagnetic shielding is legally imposed by governmental agencies to protect users from excessive amounts of electromagnetic radiation generated by the electrical and electronic components housed within the printer. In addition, some of the electronic components themselves must be shielded against stray radiation from other components in order to function properly. The same is true for the requirement of shielding against static electricity: many digital electronic components malfunction when excess static electrical charges accumulate in the vicinity of such components. In addition, many of the same components are highly sensitive in their performance to elevated temperatures and will malfunction unless the heat generated by operation of the power components, such as the AC power transformer, is conducted away.
In the past, the electromagnetic radiation and static discharge problems have been addressed by providing discreet electrically conductive shields carefully arrayed about the electronic components of the printer system. Similarly, the problem of heat generation has been addressed by providing one or more individual discreet thermally conductive masses fastened to appropriate portions of the printer support elements and the heat generating electrical power components have been attached to such devices, all of which adds additional mechanical components to the printer with the attendant cost of parts and installation.